1. Technical Field
The present invention relates to a liquid developer and an image forming method.
2. Related Art
In using developers used for developing an electrostatic latent image formed on a latent image carrier, there are a method using a dry toner in which a toner constituted with a material including a coloring agent such as a pigment and a binder resin is used in a dry state, and a method in which a liquid developer is used by dispersing a toner in a carrier liquid having an electrical insulation property (an insulating liquid).
The method using a dry toner has an advantage in treatment because the toner is handled in a solid state, but has problems in that there are concerns about adverse effects to the human body caused by the powder, flying toner particles causing contamination, and the toner particles not being uniformly dispersed. In addition, with the dry toner, there are problems that the toner particles easily clump together, it is difficult to make the size of the toner particles sufficiently small, and it is difficult to form a toner image with a high resolution. Moreover, when the size of the toner particles is relatively small, the problems caused by the powdery state as described above become more evident.
On the other hand, the method using a liquid developer enables the use of fine toner particles because the clumping of the toner particles in the liquid developer is effectively prevented, and the method can use a liquid developer having a lower softening point (low softening temperature) than a resin material used in a dry toner as a binder resin. As a result, the method using the liquid developer is excellent in reproducibility of a fine line image, reproducibility of a grayscale, reproducibility of colors, and a high speed image forming method.
However, an insulating liquid that has been used in a liquid developer in the related art mainly includes a petroleum-based hydrocarbon. In such a liquid developer, the insulating liquid adheres onto the surface of the toner particles during fixing. In the liquid developer in the related art, the insulating liquid adhering to the surface of the toner particles deteriorates fixing intensity, and thereby it is not possible to obtain a sufficiently satisfactory fixing property.
In order to solve the problem, there was an attempt to improve the fixing intensity by an oxidative polymerization reaction of a fat during the fixing, using a fat derived from the nature such as vegetable oil as the insulating liquid (JP-A-2006-251252).
However, even when the fat as above was used, it was not possible to obtain sufficient fixing intensity.